The present invention relates to containers made of paper and plastic for liquids and, more particularly, to an opening arrangement for packages of the type which comprises a double-walled triangular lug communicating with the interior of the package and being connected to one side wall of the package, and a sealing fin extending over the top side of the package and the said triangular lug.
Packing containers of the above-mentioned type are frequently manufactured by converting a packing material web consisting of a carrier layer such as paper and surface layers of thermoplastic material such as polyethylene to a tube in which the longitudinal edges of the web are combined with one another in an overlapping joint. The formed tube is filled with the intended contents, for example, milk or fruit juice, whereupon the filled tube is flattened and sealed along narrow transverse regions of the tube so as to form closed packing containers cutting through the said transverse sealing zones separate the packages into individual containers, which containers are formed previously in special forming devices in connection with, or following, the sealing and separation into packing containers of the desired shape.
When a parallelepipedic shape is imparted to any one such tube section, triangular, double-walled lugs are formed at four opposite lateral edges. The interior of each lug communicates with the interior of the package, and these lugs are folded in and sealed to the packing container. During the division of the tube into individual packing containers which, as mentioned previously, is accomplished by cutting through the transversely sealed zones, upright sealing fins are formed which are relatively rigid, since doubled packing material is sealed together within this region. The said sealing fins which extend transversely over the tube will in the finished package extend transversely over the upper end wall of the package and over the top side of the triangular lugs up to their tip.
It has been known previously that on opening of the package these triangular lugs can be used to create a pouring duct, and in general this is realized so that one of the triangular lugs, which is lightly attached to the package body, is raised by breaking the sealed union, whereupon parts of the triangular lugs can be torn off so as to produce an emptying duct. Thus, it is known that underneath the base line of the sealing fin a perforation line can be arranged which either extends along a part of the sealing fin up to the tip of the fin or extends obliquely over the triangular lug as shown in the Swedish patent specification No. 213 171.
However, it has been found that these perforation configurations have certain disadvantages. It is difficult for example in the case of the straight perforation which extends along the base line of the sealing fin up to its tip to "initiate" the tear, since the tearing should start just at the tip of the triangular lug where several wall panels converge. Furthermore, the gripping part is relatively small to keep hold of during the tearing operation. It is a further disadvantage that the straight back perforation underneath the sealing fin only furnishes a linear opening which has to be widened by shaping the wall opening by hand. Although an oblique tearing perforation does of course provide a larger permanent pouring duct, in general the duct is of such a small length along the fin that no air can enter into the package during pouring which gives rise to the so-called gurgling phenomenon. A further disadvantage of the straight perforation is that the perforation line passes through the tip of the triangular lug, where the material is subjected to very great bending, tensile and shear stresses. As a consequence of these stresses, the perforation may open spontaneously, as when the package is exposed to a shock, which would result in a leakage.
Attempts have been made to combine the types of tearing perforation configurations mentioned above by providing a "broken" perforation line have not been successful. In the first place an oblique tearing perforation has to be initiated at an angle to the edge where the tearing starts which is more difficult than starting the tearing at a right angle to the said edge line. A second, and perhaps more decisive disadvantage is that the tearing which follows the oblique perforation in general continues straight along any break in the perforation line instead of being directed to the perforation which follows the sealing fin, that is to say it is not the whole opening that is torn open but only the oblique perforation which furnishes a small emptying duct giving rise to "gurgling" problems.